High molecular weight linear polyesters and copolyesters of terephthalic and isophthalic acid are well known in the prior art. These polymers are described in the literature and in Whinfield et al., U.S. Pat. No. 3,465,319 and Pengilly, U.S. Pat. No. 3,047,539 which are hereby incorporated by reference.
The linear polyesters have been employed for various thermoplastic molding applications and in the preparation of foamed structures. While these foamed structures have good physical properties, it is advantageous to provide polyester foamed compositions that have increased toughness as shown by an increase in tests that evaluate the elongation to break properties of these compositions.
It has now been found that the use of a minor amount of a ionically crosslinked copolymer and a minor amount of a polytetrafluoroethylene resin in a foamed linear polyester composition will result in a tougher product having improved properties. Surprisingly, it has been found that not all of the ionically crosslinked copolymers are effective in increasing the toughness of foamed linear polyesters. In particular, those ionically crosslinked copolymers that are crosslinked with zinc do not produce this effect.
Therefore, it is a primary object of this invention to provide an improved foamed linear polyester composition.
It is also an object of this invention to provide a foamed linear polyester composition that has increased toughness as evaluated by tests that determine the elongation to break properties of these compositions.